Prefix fire-and-forget calls (PubSub.broadcast, Oban enqueue, Logger,
update_*, etc.) with `_ =` so dialyzer knows the return value is
intentionally discarded. Wrap a few if/case expressions whose
branches produce mixed types the same way.
No behavior changes — only explicit acknowledgement of discarded
returns.
Warnings: 242 → 88.
- add MobileSocket for token-authenticated mobile WebSocket connections
- add MobileChannel with org-level and device-level real-time events
- add /mobile/socket endpoint for iOS app connections
- add "Link Mobile App" to user dropdown menu for discoverability
- improve QR code page with numbered steps and clearer instructions
- add socket/channel tests (17 total)
